The present invention relates to turbine engines, and particularly to microturbine engines. More particularly, the present invention relates to microturbine engines having lubrication oil systems.
Microturbine engines are used to generate electricity or to provide power for other rotating equipment. Microturbine engines often include two turbines, however single turbine systems are also used. In the two-turbine system, the first turbine, or gasifier turbine, rotates under the influence of a flow of products of combustion to drive a compressor. The compressor provides a supply of compressed air for combustion within a combustor. The products of combustion leaving the combustor drive the gasifier turbine and then flow to a power turbine that drives a generator or other piece of equipment.
The gasifier turbine and compressor may reside on the same shaft. The shaft is generally supported by high-speed bearings that use lubricating oil for cooling and lubrication. The power turbine as well as any associated gearing may also require a supply of lubricating oil. Thus, microturbine engine systems generally include a lubrication oil system that is capable of providing a low-pressure supply of lubricating oil to various components.
Starting a microturbine engine requires an outside energy supply to initiate rotation of the gasifier turbine and the compressor. The compressor is then able to supply compressed air to the combustor to initiate combustion and start the engine. In single turbine systems connected to a generator, it is sometimes possible to operate the generator as a motor to start the engine. However, in two-turbine systems, the gasifier turbine is not directly coupled to the generator. Therefore, an additional power supply is required. Some systems employ a gear coupled to the gasifier shaft and driven by an external motor during start-up. The addition of a gear to the gasifier shaft is undesirable due to the high speed of the shaft and the dynamic instabilities of the rotor. Also, having the starting system physically contact the shaft during operation can create a drag on the system, which results in inefficiencies. It is therefore desirable to provide a system capable of quickly accelerating the gasifier turbine to start-up speed without the addition of complicated or expensive hardware. It is also desirable to provide a system that is not in physical contact with the gasifier turbine during operation.
Thus, according to the present invention, a microturbine engine provides a housing and a turbine including a rotary element having a shaft supported by the housing and rotatable about a rotary axis. A starter wheel is coupled to the shaft and rotatable in response to a stream of high-pressure fluid flowing from a high-pressure flow path. A pump is operable to provide a supply of lubricating fluid. The engine further includes a starter valve receiving the supply of lubricating fluid and being selectively operable to provide one of the stream of high-pressure fluid to the high-pressure flow path and a stream of low-pressure fluid to a low-pressure flow path.
The invention further provides a method of starting a microturbine engine having a compressor supported for rotation and having a starter wheel coupled to the compressor. The method comprises the acts of providing a supply of lubricating fluid with a constant displacement pump and providing a starter valve in fluid communication with the pump, the valve receiving the supply of lubricating fluid from the pump. The method further includes the steps of operating the starter valve to provide a high-pressure stream of fluid and directing the high-pressure stream to impinge upon the starter wheel to begin rotation of the compressor until the engine has started. The method also includes the steps of operating the starter valve to provide a low-pressure stream of fluid and directing at least a portion of the low-pressure stream to the microturbine engine to provide lubrication.
In preferred embodiments, a solenoid operated starter valve operates to redirect flow from the lubrication oil pump to the high-pressure flow path. The high-pressure flow path includes a pressure control valve that directs a portion of the high-pressure stream to the low-pressure flow path at a lower pressure while maintaining the desired pressure within the high-pressure flow path. The high-pressure oil flows through a nozzle and into a Pelton wheel attached to the gasifier turbine shaft. The Pelton wheel rotates in response to the oil flow accelerating the turbine and compressor. Once the engine is started, the starter valve solenoid de-energizes redirecting the oil flow through the low-pressure system at the desired lubricating oil pressure.
Additional features and advantages will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.